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The effect of long-term ageing (1000, 2000, and 3000 h) at 475 degrees C on mechanical properties, microstructure, and substructure of CUSTOM 465 (R) maraging stainless steel was studied. The additional precipitation of nanometric particles of eta-Ni3Ti phase in partly recovered lath martensite and decomposition of the BCC solid solution accompanied by the formation of nanometric Cr-rich alpha'particles were identified. The fraction of reverted austenite in the final microstructure gradually increased with time of ageing at 475 degrees C. Ageing resulted in a gradual slight decline (up to 10%) in yield strength, ultimate tensile strength, and hardness. On the other hand, for all ageing, dwells ductility and impact energy values remained almost unchanged. The reason for this phenomenon lies in the gradual increase in the fraction of reverted austenite during long-term ageing at 475 degrees C and at the same time in the sluggish kinetics of microstructural changes in lath martensite. No susceptibility to 475 degrees C embrittlement was proved. Web of Science 12 10 art. no. 1643

V minulém roce zde byl uveden příspěvek, který se zabýval mikrostrukturou a vlastnostmi trubky o tloušťce stěny 90 mm z oceli P92, u kterého byly zjištěny četné řediny, zejména v blízkosti vnitřního povrchu trubky. Řediny vznikly zřejmě v důsledku nedostatečného protváření během válcování trubky. Analýzy lokálních materiálových vlastností u obou povrchů trubek provedené tehdy jsou zde doplněny o výsledky creepových zkoušek malých vzorků (SPC testy), které doplnily creepové zkoušky do lomu prováděné na konvenčních zkušebních tyčích. Výsledky SPC testů jsou porovnány s materiálovými požadavky na ocel P92 a je proveden pokus o vyhodnocení možného vlivu nehomogenity mikrostruktury a vlastností na dlouhodobou životnost trubky v podmínkách tečení. Tento příspěvek vznikl za finanční podpory Technologické agentury České republiky v rámci projektu THÉTA TK01020160 „Komplexní postupy materiálového inženýrství k zajištění bezpečného provozu inovovaných bloků klasických elektráren“. Last year, a paper was presented here, which dealt with the microstructure and properties of pipe with a wall thickness of 90 mm made of P92 steel, in which numerous dilutions were found, especially close to the inner surface of the pipe. The dilutions were probably caused by insufficient deformation during the rolling of the pipe. Analyzes of local material properties at both pipe surfaces performed at that time are supplemented here by the results of small punch creep tests (SPC tests), which complemented the stress fracture tests performed on conventional test specimens. The results of SPC tests are compared with the material requirements for P92 steel and an attempt is made to evaluate the possible influence of inhomogeneity of the microstructure and material properties on the long-time creep exposure of the pipe.

Článek se zabývá strukturou a vlastnostmi trubky s tloušťkou stěny 90 mm vyrobené z oceli P92. Metalografická analýza odhalila četné řediny zejména u vnitřního povrchu trubky, které jsou zřejmě důsledkem nedostatečného protváření při válcování trubky. Srovnání lokálních materiálových vlastností u obou povrchů trubky bylo provedeno jednak pomocí metalografie, jednak tahovými zkouškami, zkouškami tvrdosti, zkouškami vrubové houževnatosti a penetračními zkouškami malých vzorků. Získané výsledky jsou porovnány s materiálovými požadavky na ocel P92 a doplněny úvahami o vlivu nehomogenity struktury a vlastností na dlouhodobou životnost trubky v podmínkách creepového namáhání. THÉTA TK01020160 The paper deals with the microstructure and properties of a pipe with a wall thickness of 90 mm made of P92 steel. Metallographic analysis revealed numerous dilutions, especially close to the inner surface of the pipe, which developed probably due to insufficient deformation during pipe rolling. The local material properties of both pipe surfaces were compared by metallography, tensile tests, hardness tests, Charpy-V notch toughness tests as well as penetration tests of small samples. The obtained results are compared with the material requirements for P92 steel and an attempt is made to evaluate the possible influence of the inhomogeneity of the microstructure and properties on the long-term service life of the pipe under creep conditions.

This chapter deals with the change of the structure and mechanical properties of the austenitic steels grades TP347HFG, Super 304H and HR3C as well as their welded joints after the exposure at temperatures corresponding to the ultra-super critical (USC) and advanced ultra-super critical (A-USC) parameters. Several tube bend radii were investigated in order to understand relation between cold work plastic deformation, mechanical properties and the structural changes with special attention to the generation of sigma phase during long-term high temperature exposure. The effect of post bend solution annealing work on the material properties and structural changes was studied, too, using small punch test (SPT) and miniaturized tensile tests taken both from straight part and extrados of bends under investigation. Creep properties of either base metal either welded joints were tested and evaluated using standard creep specimens at temperatures 650, 700 and 750°C. The obtained results confirmed that the mechanical properties and the structure were significantly influenced even after relatively short-time exposure at elevated temperature. The results of experiments were compared with other results obtained from analyses of tubes after 100,000 h of exposure in a USC block where extensive precipitation of sigma phase was also identified.